Electromagnetic actuator for providing a hard stop for moving blade aperture systems

ABSTRACT

An hard stop for use with an aperture mechanism includes at least one blade moveable along a path between a closed position and at least one open position. At least one hard stop piston is moveable between a first position, out of the blade path, and a second position, in the blade path, to position the blade in the open position when an edge of the blade contacts the hard stop piston. The hard stop includes a magnetic piston, an electromagnet coil proximate to the magnetic piston, and a ferromagnetic ring arranged such that when current is applied in one direction through the coil it causes the magnetic piston to move to the first position in a first direction and held in such position by the attraction of the magnetic piston to the ferromagnetic ring and causes the magnetic piston to move to the second position when current is applied in an opposite direction to the coil and the magnetic piston is held in such position by the attraction of the magnetic piston to the ferromagnetic ring.

CROSS REFERENCE TO RELATED APPLICATIONS

The present invention is related to commonly assigned U.S. patentapplication Ser. No. 08/655,366, filed May 30, 1996, entitled"Electromagnetic Mechanism for Providing a Hard Stop for Moving BladeAperture Systems", by Furlani et al, now U.S. Pat. No. 5,619,296 andcommonly assigned U.S. patent application Ser. No. 08/751,597 filedconcurrently herewith, entitled "Electromagnetic Device for Providing aHard Stop for Moving Blade Aperture Systems" by Furlani et al, thedisclosures of which are incorporated herein by reference.

CROSS REFERENCE TO RELATED APPLICATIONS

The present invention is related to commonly assigned U.S. patentapplication Ser. No. 08/655,366, filed May 30, 1996, entitled"Electromagnetic Mechanism for Providing a Hard Stop for Moving BladeAperture Systems", by Furlani et al, now U.S. Pat. No. 5,619,296 andcommonly assigned U.S. patent application Ser. No. 08/751,597 filedconcurrently herewith, entitled "Electromagnetic Device for Providing aHard Stop for Moving Blade Aperture Systems" by Furlani et al, thedisclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates generally to the field of photography and, moreparticularly, to an improved electromagnetic actuated hard stop havingutility in aperture blade type mechanisms.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 4,760,420, entitled, "Shutter Mechanism For A Camera" byLam, discloses a camera shutter mechanism having overlapping plateswhich are pivotally mounted and connected by a pin sliding in slots inthe plates so that the plates move in unison. Springs bias the plates toan overlapping position, covering a hole in the camera body which leadsto a lens. One of the plates is struck by a lever which urges the platesagainst springs causing them to pivot away, until the lever strikes astop at which point the plates still overlap sufficiently to cover thehole. After the lever strikes the stop the plates continue to move undertheir own momentum to open up an aperture bound by the edges.

A magnetic control plate with pawls is attracted towards the overlappingplates by an electromagnet so that the pawls engage racks on the platesto arrest the plates at a particular aperture setting. A light meteringdevice or optical sensor is used to determine the position of the platesand thereby to control energization of the electromagnet. Theelectromagnet must be energized slightly before the desired aperture isreached to allow time for the magnetic control plate to move into theengaged position. When the electromagnet is switched off, theoverlapping plates are released which closes the aperture under theaction of the springs.

An improvement in the type of shutter shown in the U.S. Pat. No.4,760,420 patent is disclosed in U.S. Pat. No. 5,432,576, entitled,"Aperture Mechanism Having A Blade Positionable In An Open Position By AHard Stop" by SanGregory et al. In that patent hard stops are used todefine the limits of travel for the aperture plates. The hard stops arepositioned in their stopping position by activating an electromagnetthat in turn projects a magnet (piston) into the path of the blade. Tomaintain the piston in that position the electromagnet remainsenergized. To retract the piston the current flowing through theelectromagnet is reversed.

SUMMARY OF THE INVENTION

It is an object of the present invention to minimizing the current drawthat is needed to actuate and to hold the piston in place as the currentis drawn, generally, from a battery.

This object is achieved by an improved hard stop for use with anaperture mechanism that is comprised of at least one blade moveablealong a path between a closed position and at least one open position,and at least one hard stop piston that is moveable between a firstposition, out of the blade path, and a second position, in the bladepath, to position the blade in the open position when an edge of theblade contacts the hard stop piston, wherein the improved hard stop iscomprised of:

a magnetic piston;

electromagnet means including a coil proximate to the magnetic pistonand a ferromagnetic ring arranged such that when current is applied inone direction through the coil it causes the magnetic piston to move tothe first position in a first direction and held in such position by theattraction of the magnetic piston to the ferromagnetic ring and causesthe magnetic piston to move to the second position when current isapplied in an opposite direction to the coil and the magnetic piston isheld in such position by the attraction of the magnetic piston to theferromagnetic ring.

ADVANTAGES

The hard stop of the present invention has a greatly reduced powerconsumption relative to the current hard stop mechanisms. Additionally,the present hard stop is highly reliable, and easy to manufacture. Byusing a ferromagnetic ring, separate magnets for maintaining themagnetic piston in its first or upper position or its second or lowerposition are no longer necessary.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-5 are top views of a prior art aperture mechanism wherein thepresent invention finds particular utility;

FIGS. 6A and 6B illustrate, in perspective and cross sectional views,the position of the hard stop of the present invention in itsnon-stopping position;

FIGS. 7A and 7B illustrate, in perspective and cross sectional views,the position of the hard stop of the present invention in its stoppingposition; and

FIG. 8 illustrates, in schematic form, the electronics for controllingthe hard stop actuator of the present invention.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1 and 2 which show top views of one embodiment ofthe present invention. A pair of aperture blades (blades 1 and 2), aredisplayed in a closed position in FIG. 1. In this position, blades 1 and2 block light from passing through a camera aperture 6. In FIG. 2 theblades are shown in the fully opened position (aperture 6 is fullyuncovered). An actuator 3, used to rotate blade 1, includes an arm 4 towhich is connected a pin 4a that fits through a slot 11 in blade 1. Apivot point 8 for blade 1 lies along the axis of rotation for actuator3. Thus, blade 1 directly follows the rotation of actuator 3.

A link 14 acts as a pivot point for blade 2 at a position 9. Link 14includes a pin 5 and an arm 14a to which the pin is connected. Pin 5fits through slots (apertures) 12 and 13 of blades 2 and 1 respectively,thus rotating with blade 2 as it causes blade 2 to follow the motion ofblade 1 at this point. It can be seen that as blade 1 rotates clockwiseblade 2 is caused to rotate counter-clockwise and vice-versa. Hard stoppistons, 7a, 7b, and 7c, will be described in detail in the descriptionof FIGS. 3, 4, and 5.

Actuator 3 is preferably a rotary magnetic actuator or solenoid.Magnetic attraction torque within actuator 3 keeps the blades rotated tothe closed condition when the actuator is not energized. Energizingactuator 3 to rotate clockwise drives the blades opened, as describedabove. Energizing actuator 3 to turn counter-clockwise returns theblades to the closed condition after proper exposure.

The present invention varies aperture size by using moving hard stoppiston to position the blades at discrete degrees of travel. FIGS. 3, 4and 5 show the shutter opened to three intermediate apertures. In FIG.3, a hard stop piston 7a, normally out of a plane of rotation of blade2, is placed in the path of blade 2 to stop the shutter from furtheropening. Thus, the blades together form an exposure aperture area 15.The geometry of blades 1 and 2 and the position of hard stop pistons7a-c are selected to minimize bounce of the blades when they strike thepistons.

In FIG. 4, a hard stop piston 7b blocks the path of blade 1, thusexposing an area 16. Piston 7a is not placed in the path of blade 2 inthis case or else the blades would stop as shown in FIG. 3. In FIG. 5, apiston 7c stops the shutter to expose area 17. Again, the other twopistons are not employed for this condition and are located out of theplane of rotation of their respective blades.

The hard stop pistons described in the previous paragraphs arepreferably made of a permanent magnetic material. These hard stoppistons are moved into the shutter blade path by a magnetic force fromnearby coils which are selectively energized. One magnetic hard stoppiston is used for each partial aperture (one less than the total numberof apertures).

Referring now to FIGS. 6A and 6B, a hard stop 7 is comprised of anelectromagnet 21 that is formed by a coil which has two counter-woundportions 21A and 21B supported on a plastic housing 23. The housing 23mounts to the camera or other device that incorporates the presentinvention. The piston, 7a, 7b, or 7c, of the hard stop 7 is formed as acylindrical rod comprising a permanent magnet 36A and a non-magneticmaterial such as a plastic rod 36B. Although the electromagnet 21 andthe piston 7a, 7b, or 7c are cylindrically shaped in cross-section it isunderstood that other shapes may be utilized without detracting from theinvention. A non-magnetic plate 20 having an aperture 26 therein forreceiving the end of the piston 7a, 7b, or 7c with the magnet 36A, andpositioned to support the shutter blades 1 and 2 in a plane that istransverse to the movement of the piston 7a, 7b, or 7c. A ferromagneticring 28 is secured to the coil having counter-wound portions 21A and21B. It is instructive to note that, in the position shown in FIG. 6B,the magnet 36A is held stationary against the lower stop 23A of theplastic housing 23 by the dominant magnetic attraction of the North poleof magnet 36A to the ferromagnetic ring 28.

Referring to FIGS. 7A and 7B, a source of current (shown in FIG. 8),causes current to flow through the coil having counter-wound portions21A and 21B in a first direction which propels the piston 7a, 7b, or 7cinto the aperture 26 which in turn limits (stops) the movement of theshutter blade 1 (shown clearly in FIG. 7A). The motion of the piston 7a,7b, or 7c in response to the current can be understood by consideringthe interaction of the magnetic field of the electromagnet 21 with themagnetic poles of magnet 36A. Specifically, the coil portion 21Aproduces a magnetic field substantially along its axis that imparts anupward force in the north pole of magnet 36A. In a similar fashion, thecoil portion 21B produces a magnetic field substantially along its axisthat imparts an upward force to the south pole of magnet 36A. The magnet36A moves upwards in response to these forces. When the piston 7a, 7b,or 7c is in this position, the magnet 36A is still held stationaryagainst insert 40, which is fastened to plastic housing 23 with pins 41and 42, via the dominant magnetic attraction of the South pole of magnet36A to the ferromagnetic ring 28. The piston 7a, 7b, or 7c is held inthis position after the current stops flowing through the coil havingcounter-wound portions 21A and 21B. As such the stopping functionremains in effect without requiting a sustaining current. To move thepiston 7a, 7b, or 7c to the nonstopping position the current through thecoil having counter-wound portions 21A and 21B is reversed which in turnattracts the piston 7a, 7b, or 7c back into the plastic housing 23,shown in FIGS. 6A and 6B.

Referring now to FIG. 8, the control of the current flow through theelectromagnet 21 is adjusted by the circuitry 30. A shutter button 32provides the initial activation signal to a control circuit 53. Anadditional input is provided by a photometric sensor 50 which suppliesan output indicating a low or a high amount of light being presented tothe aperture mechanism. If a low amount of light is present the pistonshould not stop the blade. If a high amount of light is present thepiston is to stop the blade. The control circuit 53 controls a currentdriver 54 for pulsing current through the electromagnet 21 in thedirection that causes the associated piston to take the positionindicated by the photometric sensor 50. Once in the proper position thecurrent pulse is no longer necessary to hold the piston in positionwhich provides the major advantage of the present invention namely toreduce the amount of current needed for each shutter operation.

The invention has been described with reference to preferredembodiments. However, it will be appreciated that variations andmodifications can be effected by a person of ordinary skill in the artwithout departing from the scope of the invention.

PARTS LIST

1,2 aperture blades

3 actuator

4 arm

4a, 5 pins

6 aperture

7 hard stop

7a-c hard stop pistons

8 pivot point

9 position

11 slot

12, 13 slots

14 link

14a arm

15, 16, 17 aperture area

20 non-magnetic plate

21 electromagnet

21A, 21B counter-wound coil portions

22 steel plate

23 plastic housing

23A stop

26 aperture

28 ferromagnetic ring

30 circuitry

32 shutter button

36A magnet

36B plastic rod

40 insert

41 pin

42 pin

50 photometric sensor

53 control circuit

54 current driver

We claim:
 1. A hard stop for use with an aperture mechanism that iscomprised of at least one blade moveable along a path between a closedposition and at least one open position, and at least one hard stoppiston that is moveable between a first position, out of the blade path,and a second position, in the blade path, to position the blade in theopen position when an edge of the blade contacts the hard stop piston,wherein said improved hard stop is comprised of:a magnetic piston;electromagnet means including a coil proximate to said magnetic pistonand a ferromagnetic ring arranged such that when current is applied inone direction through the coil it causes the magnetic piston to move tothe first position in a first direction and held in such position by theattraction of the magnetic piston to the ferromagnetic ring and causessaid magnetic piston to move to the second position when current isapplied in an opposite direction to the coil and said magnetic piston isheld in such position by the attraction of the magnetic piston to theferromagnetic ring.
 2. The hard stop of claim 1 wherein said magneticpiston moves in a direction essentially perpendicular to said path ofmovement of said blade when said piston moves between the first and thesecond positions.
 3. The hard stop of claim 1 wherein said magneticpiston is formed of a magnetic central portion with a non-magneticporiton on one side of the magnetic central portion.
 4. The hard stop ofclaim 3 and further comprising a non-magnetic material positioned on atleast one end of said magnetic central portion.
 5. The hard stop ofclaim 1 wherein said coil includes two counter-wound portions defining acentral opening.
 6. The hard stop of claim 5 wherein said magneticpiston is formed as an elongated cylinder that is positioned within thecentral opening.
 7. The hard stop of claim 1 and furthercomprising:control means responsive to an input for applying a currentto said electromagnet means in said first direction upon receipt of afirst input and for applying a current to said electromagnet means insaid second direction upon receipt of a second input.
 8. The improvedhard stop of claim 7 and further comprising a photometric means forsensing light to be controlled by the aperture mechanism for providingsaid first input to said control means when the level of light is abovea first level and for providing said second input to said control meanswhen the level of light is below said first level.